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Biomedical subjects

S J Walter

Publications and source records attributed to S J Walter.

At least 55 records · Page 3Linked to original sources
PubMed1981

The effect of vasopressin on extracellular cation concentrations and muscle resting potentials in the rat.

1. The Na+ and K+ concentrations in plasma and cerebrospinal (c.s.f.), resting potentials in skeletal muscle fibres, cardiac beat to beat intervals and 90% repolarization times were measured in Long Evans rats (parent strain controls) and in Brattleboro rats with hypothalamic diabetes insipidus (DI). 2. Cation concentration measurements confirmed previous observations that Brattleboro DI rats are mildly hypokalaemic compared with rats of the parent Long Evans strain, and indicated that the c.s.f. [Na+] is significantly raised in the former group of animals while the [K+] in the c.s.f. samples is similar in the two groups. 3. The mean resting potential of deep skeletal muscle fibres in Brattleboro DI rats was significantly more negative than the corresponding value in the Long Evans rats, and this finding was in close agreement with the difference observed for the calculated K+ equilibrium potentials in the two groups of animals. 4. The beat to beat intervals and the 90% repolarization times of cardiac action potentials were also determined in Brattleboro DI and Long Evans rats, and the mean values for both variables were significantly shorter in the former group of animals. 5. The administration of Pitressin by subcutaneous injection (500-100 mu./24 hr) to Brattleboro rats abolished the hypokalaemia and the hyperpolarization of skeletal muscle fibre membranes but had no significant effect on c.s.f. cation concentrations. 6. The present findings suggest that the absence of vasopressin in the Brattleboro DI rats results in a hyperpolarization of muscle cell membranes, and in changes in the cardiac action potential. These effects may be partly related to the mild hypokalaemia present in these animals.

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PubMed1979

The role of vasopressin in blood pressure regulation immediately following acute haemorrhage in the rat.

1. The possible pressor effect of vasopressin immediately after acute haemorrhage has been studied using anaesthetized Brattleboro rats with diabetes insipidus and rats of the Long Evans parent strain.2. A blood loss of 0.5% of the body weight caused a significant decrease in mean arterial blood pressure, measured 10 min later, in Brattleboro rats, whereas this degree of haemorrhage was non-hypotensive in the control Long Evans rats. Following subsequent blood losses (each of 0.5% of the body weight), mean arterial blood pressure in Brattleboro rats was always significantly lower than in Long Evans rats.3. While no antidiuretic activity was at any time found in the plasma of Brattleboro rats, haemorrhages greater than 1% of the body weight were associated with marked increases in plasma arginine vasopressin (AVP) of Long Evans rats.4. When Brattleboro and Long Evans rats were subjected to a single haemorrhage of 2% of the body weight, the immediate decrease in arterial blood pressure was similar in the two groups. However, 5 and 10 min after the haemorrhage the arterial blood pressure was significantly higher in the Long Evans rats. When vasopressin was infused into Brattleboro rats so that plasma levels of the hormone approached those found in Long Evans rats, the mean arterial blood pressure 0, 5 and 10 min after haemorrhage was similar to that in the Long Evans animals.5. It is concluded that in the anaesthetized rat, vasopressin plays an important role in the regulation of arterial blood pressure during the period immediately following acute haemorrhage.

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PubMed1978

The role of sodium depletion in hydrochlorothiazide-induced antidiuresis in Brattleboro rats with diabetes insipidus.

1. The mechanism of the antidiuretic effect of hydrochlorothiazide in diabetes insipidus was studied in anaesthetized Brattleboro rats with the hereditary hypothalamic form of the disease. 2. The antidiuresis caused by acute administration of hydrochlorothiazide followed an increase in sodium excretion and was associated with a significant fall in the plasma sodium concentration. There were concomitant falls in effective renal plasma flow and glomerular filtration rate. 3. When sodium depletion was prevented by adjusting the infusion of sodium chloride, the falls in plasma sodium concentration, effective renal plasma flow and glomerular filtration rate were abolished. Under these circumstances there was an increase in urine volume, which suggests that hydrochlorothiazide may inhibit fractional fluid reabsorption in the proximal convoluted tubule. 4. The results indicate that the antidiuresis caused by hydrochlorothiazide in diabetes insipidus results, at least in part, from falls in effective renal plasma flow and glomerular filtration rate. These in turn seem to be entirely secondary to the drug-induced sodium depletion.

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PubMed1977

Immunogenic contaminants in mouse nerve-growth factor.

Experiments are described that confirm the presence of gamma-globulin in standard preparations of mouse nerve growth factor (7-S complex and beta subunit) and show that antibodies to this protein are present in horse antisera to the growth factor. These antibodies may be partially removed by adsorption with soluble antigen and totally removed by affinity chromatography on columns of insolubilised antigen. These procedures do not affect the potency of the antiserum in vitro or in vivo. Contaminating globulin may be removed from samples of the isolated beta subunit by gel filtration to give an immunochemically pure preparation which will permit more meaningful studies on nerve growth factor and its antiserum.

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PubMed1977

The effects of postganglionic axotomy and nerve growth factor on the superior cervical ganglia of developing mice.

Sectioning of the two major outflows from the superior cervical ganglia in two week mice results in a marked drop in the number of neurons within one week of operation and a smaller drop over the following two weeks. In animals receiving daily injections of nerve growth factor (NGF), the effect of axotomy is modified. One week after axotomy, the number of neurons in the axotomized ganglia is approximately the same in NGF treated animals as in the control, sham operated ganglia. Over the next two weeks, however, the cell death that results from axotomy is no longer prevented by treatment with NGF. The normal, hyperplastic response to NGF appears to occur independently of the cell reaction caused by axotomy.

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PubMed1975

Effects of nerve growth factors from mouse salivary glands and snake venom on the sympathetic ganglia of neonatal and developing mice.

1. Quantitative histological analysis has been made of the effects of nerve growth factor (NGF) from mouse submaxillary gland and from the venom of Vipera russelli on superior cervical ganglia of neonatal mice. 2. The hypertrophic and hyperplastic effects reported by other workers have been confirmed. 3. The hypertrophic effect arises from an increase in the rate at which the sympathetic neurones attain their mature size. The size at maturity is never exceeded. 4. The hyperplastic effect arises from an increase in the rate of production of neurones from less differentiated cells. In the developmental period, the number of neurones can exceed that found at maturity. If injection of NGF is discontinued the excess neurones disappear. 5. If injection of NGF is continued to maturity, the excess number of neurones is maintained.

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PubMed1973

Protein fractions from mouse salivary glands affecting epithelial cells in organ culture.

1. Extracts of male mouse submaxillary gland have been fractionated on G 150 Sephadex and DEAE cellulose.2. A number of the protein fractions obtained appear to cause proliferation of epithelial cells in organ cultures of rat tissues.3. All fractions active in organ culture possess proteolytic enzyme activity.4. The proteolytic enzymes trypsin, pronase and collagenase produce epithelial disorganization in organ culture.5. The organ culture effect is reduced in the presence of proteolytic enzyme inhibitors and abolished by pretreatment of proteins with diisopropylfluorophosphonate.6. The presence of mitotic inhibitors does not reduce the organ culture effect.7. The effect is not associated with an increase in the DNA content of tissue explants.8. No evidence has been found for the existence, in mouse salivary glands, of a specific growth factor acting on epithelial cells.

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